1 research outputs found
Fluorescence Sensing Mechanisms of Versatile Graphene Quantum Dots toward Commonly Encountered Heavy Metal Ions
Graphene quantum dots (GQDs) have received tremendous
attention
as fluorescent probes for detection of diverse heavy metal ions (HMIs).
Nevertheless, the fluorescence sensing mechanisms of versatile GQDs
with respect to different HMIs remain elusive. Herein, the fluorescence
sensing behaviors and mechanisms of GQDs with amino and carboxyl groups
toward commonly encountered Cr6+, Fe3+, Cu2+, Cr3+, Mn2+, Co2+, Ni2+, Zn2+, Cd2+, and Hg2+ under
different pH conditions are systemically explored. The results show
that the fluorescence of GQDs can be enhanced by Zn2+/Cd2+ and quenched by other HMIs at pH 5.8, while it can be enhanced
by HMIs except Cr6+/Fe3+/Cu2+ at
pH 2.0. Systematic studies verify that the fluorescence quenching/enhancing
is mediated by the synergistic effect of the inner filter effect (IFE)
and the photoinduced electron transfer (PET) or metal orbital-controlled
chelation-quenched/enhanced fluorescence (CHQF/CHEF) effect. The strong
and weak IFEs of Cr6+/Fe3+ and Cr3+/Cu2+, respectively, are one of the reasons for the fluorescence
quenching, while other HMIs have no IFE. Moreover, the PET effect
caused by the interaction of GQDs with Hg2+ at pH 5.8 and
the CHQF/CHEF effect caused by the interaction of GQDs with other
HMIs are also crucial for fluorescence quenching/enhancing. The findings
suggest that the pH condition, the existing forms of functional groups
on GQDs, and the complexation states of HMIs in aqueous systems dominate
the PET and CHQF/CHEF effects. The elucidating of the fluorescence
sensing mechanisms of GQDs toward different HMIs paves the way for
developing versatile sensing platforms for monitoring of HMI contamination